Superior accessory fissure

The superior accessory fissure is present in around 5% of individuals examined with CT ⁴. 

Gross anatomy

The superior accessory fissure of the right lower lobe is located in the same plane and posterior to the right minor fissure. It separates the right lower lobe into superior and basal segments. This superior segment is called the posterior or dorsal lobe.

The fissure varies in length from complete to incomplete fissure ^1,2. The incidence is greater with right lung involvement and less common than an inferior accessory fissure ¹.

Radiographic features

Plain radiograph

Frontal chest radiographs demonstrate a thin horizontal linear opacity projecting below, parallel, and medial to the right minor fissure. The lateral radiograph demonstrates a thin line posterior to the right minor fissure, usually in the same plane and in a horizontal or oblique orientation. It may look like a continuation of the right minor fissure posteriorly, which separates the right lower lobe into superior and inferior segments ^1,2.

Differential diagnosis

Consider:

• pleural-parenchymal scarring